Transformer



Feb. 5, 1929. 1,701,334

' K. K. PAL UEFF TRANSFORMER Fig.1.-

Fig.2.

Inventor Konstantin KFaluef'f, WW

His/Attorney.

'it ma 1,701,334 PATENT OFFICE.

KONSTANTIN K.

TAL'UEFE'OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

TRANSFORMER.

Application filed April 18, 1928. Serial No. 271,044.

My invention "relates to transformers and more particularly to theinsulation of high voltage transformer windings. The electrical lossesin transformers appear as heat which must be dissipated rapidly enoughto prevent excessive temperatures. Suitable ducts are therefore usuallyprovided through which cooling currents of some cooling and insulatingfluid such as air or oil may flow. The windings must be effectivelyinsulated and supported and for this purpose some suitable solidinsulating material having the necessary rigidity and mechanicalstrength is used. .These requirements often necessitate the use of twokinds of insulation, such as a solid and a fluid, arranged in seriesbetween the high and low voltage windings.

Where the high voltage winding and the low volta e winding of atransformer are separated %y two kinds of insulation arranged in series,the total voltage between the two windings will be distributed betweenthe two insulating mediums in direct proportion to their thicknesses andin inverse proportion to their permitivities or specific inductivecapacities. If the two series arranged insulating mediums are air andimpregnated pa er of a type commonly used in transformers, t en be shownthat the voltage gradient in the a1r will be approximately four times asgreat as that in the paper insulation. The dielectric strength of theair, however, is much lower than that of the paper. Now, if the totalvoltage is such that the air is subjected to its maximum safe stress,then the paper insulation may be subjected to only about one tenth ofthe maximum voltage stress which it could safely withstand. The paperinsulation would, therefore, not be used economically. If the twoinsulating mediums are impregnated paper and a type of insulatin oil inwhich transformers are often immerse then the paper insulation could besubjected to only about one quarter of its maximum safe voltage stresswithout causing the oil insulation to break down and again the paperinsulation would not be used economieally. In order to prevent abreakdown of the fluid insulation in either of these cases, a muchgreater thickness of the solid insulation is required than that whichwould otherwise be necessary for it to withstand its own volta e.

The thermal and mechanical characteristics of many transformers,particularly of those of the larger sizes, make necessary the use ofboth solid and fluid insulation arranged in series between the twowindings and for the reasons already explained an excessive amount ofsolid insulation has been used in order to prevent breakdown of thefluid insulation. The distance between the windings required for theinsulation has thus often been greater than desirable because theleakage reactance of a transformer is proportional to the distancebetween its windings. The general object of the invention is to providean improved construction and arrangement whereby both solid and fluidinsulation may be used economically and efiiciently between high and lowvoltage transformer windings so that the windings may be placedreasonably close together and a low reactance secured.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing in which Fig. 1 showsan encased oil immersed transformer having windings of the concentrictype insulated from each other in accordance with the invention, thefigure being partly in section to reveal the construction more clearly,and Fig. 2 shows a transformer, partly in section, having interleavedwindings insulated from each other in accordance with the invention.

The transformer shown in Fig. 1 includes a magnetic core 10 with a highvoltage winding 11 and a low voltage winding 12 arranged concentricallywith respect toeach other and about the winding leg 13 of the core andthe high voltage winding 11 surrounding both the low voltage winding andthe winding leg of the core. The low voltage winding 12 is insulatedfrom the winding leg 13 by an interposed insulating cylinder 14.

The high and low voltage windings are separated by a cylindrical spacecontaining a solid insulating cylinder 15 next to the high voltagewinding and a duct 16 filled with an insulating fluid next to the lowvoltage winding. The transformer is immersed-in an insulating'liquidsuch as oil in a casing 17 so that this liquid or fluid may circulatethrough the duct 16 and along the surface of the low voltage winding 12to carry away heat and prevent excessive temperature in this winding.Solid and fluid insulations having different permitivities are thusarranged 1n series between the two windings and for reasons alreadyexplained the thickness of the solid insulation and therefore thespacing of the windings and the reactance of the transformer must bemuch greater than that required by the voltage across the solidinsulation unless there is some provision to prevent breakdown of thefluid insulation.

A layer or cylinder 18 of conductive material is carried by theinsulating cylinder 15 and is preferably embedded in it between itsinner and outer surfaces. The conductive layer 18 is maintained at a lowvoltage not diflering greatly from that of the low voltage winding 12, aconvenient way of maintaining this low voltage being by a connection 19between the conductive layer 18 and the core 10 of the transformer whichis usually grounded. This conductive layer 18 will obviously protect thefluid insulation in the duct 16 from all effects of the high voltage ofthe winding 11.

The thicknesses of solid insulation on the opposite sides of theconductive layer 18 will of course depend upon the voltages of the twowindings 11 and 12 and upon the dielectric strength of the insulation.The space between the high voltage winding 11 and the conductive layer18 is completelyfilled with solid insulation which need therefore beonly thick enough towithstand the voltage across it and need not bedepended upon at all to prevent breakdown of the fluid insulation in theduct 16. The presence of the conductive layer 18 thus permits aconsiderably smaller quantity of insulation to be used so that thewindings may be considerably closer together and this results in aconsiderably reduced reactance.

Generally, if the duct 16 is thick enough for a satisfactory flow ofcooling fluid, this fluid alone may provide suflicient insulationbetween the low voltage winding 12 and the conductive layer 18. It isusually preferable, however, that there be some solid insulation toprotect the inner surface of the conductive layer. In any event, thethickness of this solid insulation, if used at all, may be small.because the voltage of the winding 12 is low.

A transformer of the interleaved winding type is shown in Fig. 2, thehigh and low voltage windings being insulated from each otherinaccordance with the invention. The high voltage winding includes twogroups of winding turns 20 instead of a single group as shown in Fig. 1.These high voltage groups of turns 20 are interposed between two spacedlow voltage groups of turns 21. Each group of low voltage turns 21 isseparated from the adjacent group of high voltage turns 20 by an annularspace containing a. duct 22 next 'to the low voltage turns for aninsulating fluid such as air or oil and a solid annular insulating ring23 next to the high voltage turns. Each solid insulating'ring 23 carriesa conductive layer 24, preferably embedded in the ring,

to prevent breakdown of the fluid insulation in the duct 22 by the highvoltage of the adjacent group of winding turns 20, each conductive layer24 also permitting efficient use of the solid insulation between it andthe adjacent high voltage group of winding turns so that the high andlow voltage turns may be reasonably close together and the reactancereasonably low.

The invention has been explained by describing and illustratingdiiferent specific forms thereof and it will be obvious that variousother modifications may be made without departing from the scope of theinvention as defined in the appended claims.

What I claim as-new and desire to secure by Letters Patent of the UnitedStates is:

1. A transformer including spaced high and low voltage groups of turns,the spacebetween said groups of turns containing two layers ofinsulation having different permitivities and arranged in series betweensaid groups of turns, and a low voltage conductive layer carried by saidinsulating layer nearest said high voltage turns.

2. A transformer including spaced high and low voltage groups of turns,the space between said groups of turns containing two layers ofinsulation having different per- 1 mitivities and arranged in seriesbetween said tween said groups of turns containing a layer of fluidinsulation next to said low voltage turns'and a layer of solidinsulation next to said high voltage turns, and a low voltage conductivelayer carried by said solid insulation and spaced from said high voltageturns.

5. A transformer including spaced high and 'low voltage groups of turns,the space between said groups of turns containing a layer offluidinsulation next to said low voltage turns and a layer of solidinsulation next tosaid high voltage turns, said solid insulation havinggreater permitivity than that of said fluid insulation, and a lowvoltage conductive layer carried by said solid insulation and spacedfrom said high voltage turns.

In witness whereof, I have hereunto set my hand this 13th day of April1928.

KONSTANTIN K. PALUEFF.

